Compression with doppler enhancement

ABSTRACT

Methods, medium, and machines which compress, enhance, encode, transmit, decode, decompress and display digital video images. Real time compression is achieved by sub-sampling each frame of a video signal, filtering the pixel values, and encoding. Real time transmission is achieved due to high levels of effective compression. Real time decompression is achieved by decoding and decompressing the encoded data to display high quality images. A receiver can alter various setting including, but not limited to, the format for the compression, image size, frame rate, brightness and contrast. In a Doppler improvement aspect of the invention, Doppler velocity scales are incorporated into grayscale compression methods using two bits. Variable formats may be selected and Doppler encoding can be turned on and off based on the image content. Frames or sets of pixels may be distinguished by automated analysis of the characteristics of an image, such as the presence of Doppler enhanced pixels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.11/638,989, filed Dec. 13, 2006 now U.S. Pat. No. 7,991,052, entitled“VARIABLE GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (ZLN),” whichhereby is incorporated by reference.

Application Ser. No. 11/638,989 is a continuation of U.S. patentapplication Ser. No. 09/467,721, filed on Dec. 20, 1999, entitled“VARIABLE GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (ZLN)”, now U.S.Pat. No. 7,233,619, which hereby is incorporated by reference.

This application, application Ser. Nos. 11/638,989, 09/467,721 claimpriority under 35 U.S.C. §119(e) of U.S. provisional application60/113,051, filed on Dec. 21, 1998, and entitled “METHODS OF ZERO LOSS(ZL) COMPRESSION AND ENCODING OF GRAYSCALE IMAGES”, which hereby isincorporated by reference.

A continuation in part of application Ser. No. 09/467,721, filed Oct.27, 2005, entitled “HANDHELD VIDEO TRANSMISSION AND DISPLAY,”application Ser. No. 11/262,106, was published as U.S. publication2006/0114987.

A continuation in part of application Ser. No. 11/262,106, filed Jun.27, 2007, entitled “HANDHELD VIDEO TRANSMISSION AND DISPLAY,”application Ser. No. 11/823,493, was published as U.S. publication2007/0247515.

A continuation in part of application Ser. No. 09/467,721, filed Jun.18, 2007, entitled “SEPARATE PLANE COMPRESSION USING A PLURALITY OFCOMPRESSION METHODS INCLUDING ZLN AND ZLD METHODS,” application Ser. No.11/820,300.

My U.S. patent application Ser. No. 09/470,566, filed on Dec. 22, 1999,and entitled “GENERAL PURPOSE COMPRESSION FOR VIDEO IMAGES (RHN)”, knownas the “RHN” method, now U.S. Pat. No. 7,016,417, hereby is incorporatedby reference. The RHN application claims a priority date based on a U.S.provisional application 60/113,276 filed on Dec. 23, 1998, which alsohereby is incorporated by reference.

The parent application Ser. No. 11/638,989 included by referenceapplication Ser. No. 09/473,190, filed on Dec. 20, 1999, entitled“ADDING DOPPLER ENHANCEMENT TO GRAYSCALE COMPRESSION (ZLD).” Co-pendingapplication Ser. No. 11/820,300, also includes and claims subject matterfrom application Ser. No. 09/473,190. Application Ser. No. 09/473,190hereby is included by reference. Application Ser. No. 09/473,190 claimspriority based on provisional application 60/113,050 filed on Dec. 21,1998 and entitled “METHODS OF ADDING DOPPLER ENHANCEMENT TO GRAYSCALECOMPRESSION (ZLD),” which is hereby incorporated by reference.

This application, application Ser. Nos. 11/820,300, and 09/473,190 claimpriority under 35 U.S.C. §119(e) of the U.S. provisional application60/113,050 filed on Dec. 21, 1998

My U.S. patent application Ser. No. 09/312,922, filed on May 17, 1999,entitled “SYSTEM FOR TRANSMITTING VIDEO IMAGES OVER A COMPUTER NETWORKTO A REMOTE RECEIVER,” now U.S. Pat. No. 7,257,158, describes anembodiment of the invention of the RHN method, as well as a system forpracticing the compression method, and also hereby is incorporated byreference.

U.S. patent application Ser. No. 09/436,432, filed on Nov. 8, 1999, andentitled “SYSTEM FOR TRANSMITTING VIDEO IMAGES OVER A COMPUTER NETWORKTO A REMOTE RECEIVER,” now U.S. Pat. No. 7,191,462, is wholly owned bythe inventor of the present invention.

ZLN is a three-letter identifier used to refer to the family ofcompression methods disclosed in the ZLN application. ZLD is athree-letter identifier used to refer to the family of compressionsmethods disclosed herein. ZL originally stood for ZeroLoss, a trademarkof Kendyl Roman referring to the clinically lossless nature of themethods. The N in ZLN refers to the variable nature of the method when Ncan be one of a plurality of values. The D in ZLD refers to the addedcapabilities for handling Doppler enhanced images in conjunction with acompression method such as one of the ZLN family of methods.

The ZLN and ZLD family of compression methods can be practiced on anynumber apparatus or medium known in the art, including those disclosedherein, in U.S. provisional application 60/085,818, internationalapplication PCT/US99/10894, international publication number WO99/59472, U.S. application Ser. No. 09/312,922, U.S. Pat. No. 7,257,158,or in U.S. patent application Ser. No. 09/436,432, U.S. Pat. No.7,191,462.

U.S. patent application Ser. No. 09/433,978, filed on Nov. 4, 1999, andentitled “GRAPHICAL USER INTERFACE INCLUDING ZOOM CONTROL REPRESENTINGIMAGE AND MAGNIFICATION OF DISPLAYED IMAGE”, now U.S. Pat. No.6,803,931, is wholly owned by the inventor of the present invention.

BACKGROUND

1. Field of the Invention

This invention relates to data compression, specifically to thecompression and decompression of video images.

The ZLD format relates specifically to the compression and decompressionof video images that contain an image overlaid with Doppler enhancement.

2. Description of Prior Art

In the last few years, there have been tremendous advances in the speedof computer processors and in the availability of bandwidth of worldwidecomputer networks such as the Internet. These advances have led to apoint where businesses and households now commonly have both thecomputing power and network connectivity necessary to havepoint-to-point digital communications of audio, rich graphical images,and video. However the transmission of video signals with the fullresolution and quality of television is still out of reach. In order toachieve an acceptable level of video quality, the video signal must becompressed significantly without losing either spatial or temporalquality.

A number of different approaches have been taken but each has resultedin less than acceptable results. These approaches and theirdisadvantages are disclosed by Mark Nelson in a book entitled The DataCompression Book, Second Edition, published by M&T Book in 1996. MarkMorrision also discusses the state of the art in a book entitled TheMagic of Image Processing, published by Sams Publishing in 1993.

Video Signals

Standard video signals are analog in nature. In the United States,television signals contain 525 scan lines of which 480 lines are visibleon most televisions. The video signal represents a continuous stream ofstill images, also known as frames, which are fully scanned, transmittedand displayed at a rate of 30 frames per second. This frame rate isconsidered full motion.

A television screen has a 4:3 aspect ratio.

When an analog video signal is digitized, each of the 480 lines issampled 640 times, and each sample is represented by a number. Eachsample point is called a picture element, or pixel. A two dimensionalarray is created that is 640 pixels wide and 480 pixels high. This640×480 pixel array is a still graphical image that is considered to befull frame. The human eye can perceive 16.7 thousand colors. A pixelvalue comprised of 24 bits can represent each perceivable color. Agraphical image made up of 24-bit pixels is considered to be full color.A single, second-long, full frame, full color video requires over 220millions bits of data.

The transmission of 640×480 pixels×24 bits per pixel times 30 framesrequires the transmission of 221,184,000 million bits per second. A T1Internet connection can transfer up to 1.54 million bits per second. Ahigh-speed (56 Kb) modem can transfer data at a maximum rate of 56thousand bits per second. The transfer of full motion, full frame, fullcolor digital video over a T1 Internet connection, or 56 Kb modem, willrequire an effective data compression of over 144:1, or 3949:1,respectively.

A video signal typically will contain some signal noise. In the casewhere the image is generated based on sampled data, such as anultrasound machine, there is often noise and artificial spikes in thesignal. A video signal recorded on magnetic tape may have fluctuationsdue the irregularities in the recording media. Florescent or improperlighting may cause a solid background to flicker or appear grainy. Suchnoise exists in the real world but may reduce the quality of theperceived image and lower the compression ratio that could be achievedby conventional methods.

Basic Run-length Encoding

An early technique for data compression is run-length encoding where arepeated series of items are replaced with one sample item and a countfor the number of times the sample repeats. Prior art shows run-lengthencoding of both individual bits and bytes. These simple approaches bythemselves have failed to achieve the necessary compression ratios.

Variable Length Encoding

In the late 1940s, Claude Shannon at Bell Labs and R. M. Fano at MITpioneered the field of data compression. Their work resulted in atechnique of using variable length codes where codes with lowprobabilities have more bits, and codes with higher probabilities havefewer bits. This approach requires multiple passes through the data todetermine code probability and then to encode the data. This approachalso has failed to achieve the necessary compression ratios.

D. A. Huffman disclosed a more efficient approach of variable lengthencoding known as Huffman coding in a paper entitled “A Method forConstruction of Minimum Redundancy Codes,” published in 1952. Thisapproach also has failed to achieve the necessary compression ratios.

Arithmetic, Finite Context, and Adaptive Coding

In the 1980s, arithmetic, finite coding, and adaptive coding haveprovided a slight improvement over the earlier methods. These approachesrequire extensive computer processing and have failed to achieve thenecessary compression ratios.

Dictionary-Based Compression

Dictionary-based compression uses a completely different method tocompress data. Variable length strings of symbols are encoded as singletokens. The tokens form an index to a dictionary. In 1977, AbrahamLempel and Jacob Ziv published a paper entitled, “A Universal Algorithmfor Sequential Data Compression” in IEEE Transactions on InformationTheory, which disclosed a compression technique commonly known as LZ77.The same authors published a 1978 sequel entitled, “Compression ofIndividual Sequences via Variable-Rate Coding,” which disclosed acompression technique commonly known as LZ78 (see U.S. Pat. No.4,464,650). Terry Welch published an article entitled, “A Technique forHigh-Performance Data Compression,” in the June 1984 issue of IEEEComputer, which disclosed an algorithm commonly known as LZW, which isthe basis for the GIF algorithm (see U.S. Pat. Nos. 4,558,302,4,814,746, and 4,876,541). In 1989, Stack Electronics implemented a LZ77based method called QIC-122 (see U.S. Pat. Nos. 5,532,694, 5,506,580,and 5,463,390).

These lossless (method where no data is lost) compression methods canachieve up to 10:1 compression ratios on graphic images typical of avideo image. While these dictionary-based algorithms are popular, theseapproaches require extensive computer processing and have failed toachieve the necessary compression ratios.

JPEG and MPEG

Graphical images have an advantage over conventional computer datafiles: they can be slightly modified during thecompression/decompression cycle without affecting the perceived qualityon the part of the viewer. By allowing some loss of data, compressionratios of 25:1 have been achieved without major degradation of theperceived image. The Joint Photographic Experts Group (JPEG) hasdeveloped a standard for graphical image compression. The JPEG lossy(method where some data is lost) compression algorithm first divides thecolor image into three color planes and divides each plane into 8 by 8blocks, and then the algorithm operates in three successive stages:

-   -   (a) A mathematical transformation known as Discrete Cosine        Transform (DCT) takes a set of points from the spatial domain        and transforms them into an identical representation in the        frequency domain.    -   (b) A lossy quantization is performed using a quantization        matrix to reduce the precision of the coefficients.    -   (c) The zero values are encoded in a zig-zag sequence (see        Nelson, pp. 341-342).

JPEG can be scaled to achieve higher compression ratios by allowing moreloss in the quantization stage of the compression. However this lossresults in certain blocks of the image being compressed such that areasof the image have a blocky appearance and the edges of the 8 by 8 blocksbecome apparent because they no longer match the colors of theiradjacent blocks. Another disadvantage of JPEG is smearing. The trueedges in an image get blurred due to the lossy compression method.

The Moving Pictures Expert Group (MPEG) uses a combination of JPEG basedtechniques combined with forward and reverse temporal differencing. MPEGcompares adjacent frames and, for those blocks that are identical tothose in a previous or subsequent frame, only a description of theprevious or subsequent identical block is encoded. MPEG suffers from thesame blocking and smearing problems as JPEG.

These approaches require extensive computer processing and have failedto achieve the necessary compression ratios without unacceptable loss ofimage quality and artificially induced distortion.

QuickTime: CinePak, Sorensen, H.263

Apple Computer, Inc. released a component architecture for digital videocompression and decompression, named QuickTime. Any number of methodscan be encoded into a QuickTime compressor/decompressor (codec). Somepopular codecs are CinePak, Sorensen, and H.263. CinePak and Sorensenboth require extensive computer processing to prepare a digital videosequence for playback in real time; neither can be used for livecompression. H.263 compresses in real time but does so by sacrificingimage quality resulting in severe blocking and smearing.

Fractal and Wavelet Compression

Extremely high compression ratios are achievable with fractal andwavelet compression algorithms. These approaches require extensivecomputer processing and generally cannot be completed in real time.

Sub-sampling

Sub-sampling is the selection of a subset of data from a larger set ofdata. For example, when every other pixel of every other row of a videoimage is selected, the resulting image has half the width and half theheight. This is image sub-sampling. Other types of sub-sampling includeframe sub-sampling, area sub-sampling, and bit-wise sub-sampling.

Image Stretching

If an image is to be enlarged but maintain the same number of pixels perinch, data must be filled in for the new pixels that are added. Variousmethods of stretching an image and filling in the new pixels to maintainimage consistency are known in the art. Some methods known in the artare dithering (using adjacent colors that appear to be blended color),and error diffusion, “nearest neighbor”, bilinear and bicubic.

Doppler Enhancement

Doppler techniques are used to determine the velocities of one or moresmall objects. Some common uses of Doppler techniques include withoutlimitation:

-   -   1. Radar used to detect rain    -   2. Radar used to determine speed of vehicles or aircraft    -   3. Ultrasound blood flow analysis

Doppler velocity scales are often incorporated with grayscale images.

In the case of ultrasound blood flow analysis, average velocities towardthe sensing probe are encoded as a shade of red and velocities away fromthe sensing probe are encoded as a shade of blue. Although the imageappears to be in color, there are really three monochromic values: agrayscale, a red scale, and a blue scale. The base image plane(grayscale ultrasound) is generated more often (typically 15-30 framesper second) than the overlay plane showing the Doppler red and bluescales (typically 3-10 frames per second).

In the case of rain, the base map of the earth is generated only onceand the Doppler colors that indicate the intensity of the precipitationare laid over the base map.

Moving Pictures

A video or movie is comprised of a series of still images that, whendisplayed in sequence, appear to the human eye as a live motion image.Each still image is called a frame. Television in the USA displaysframes at the rate of 30 frames per second. Theater motion pictures aredisplayed at 24 frames per second. Cartoon animation is typicallydisplayed at 8-12 frames per second.

Compression Methods

The ZLN and ZLD methods are effective ways to compress video images.Other compression algorithms are known in the prior art, including RLE,GIF (LZW), MPEG, Cinepak, Motion-JPEG, Sorensen, Fractal, and manyothers.

Each of these methods treats a frame of video as a basic unit ofcompression applying the compression method uniformly to the entireimage.

Color Plane Separation

It is well known in the art that an image can be uniformly separatedinto color planes based on the red, green, and blue components valuesfor each pixel, based on hue, saturation, and brightness componentvalues for each pixel, or based on ink colors, such as cyan, yellow,magenta, and black. However these color plane separations are not doneto reduce data size or to aid compression. They are used to facilitatethe display (such as on a RGB or YUV computer monitor) or the printingof the image (for example, four-color printing).

Frame Differencing

MPEG and some other compression methods compare adjacent frames in astream of frames. Under certain circumstances these methods send only asubset of a frame (namely a rectangular portion that contains a changewhen compared to the adjacent frame) which is then overlaid on theunchanged data for the adjacent frame.

SUMMARY OF THE INVENTION

In accordance with the present invention a method of compression of avideo stream comprises steps of sub-sampling a video frame, andrun-length encoding the sub-sampled pixel values, whereby the method canbe executed in real time and the compressed representation of pixelssaves substantial space on a storage medium and requires substantiallyless time and bandwidth to be transported over a communications link.The present invention includes a corresponding method for decompressingthe encoded data.

Doppler velocity scales are incorporated into grayscale compressionmethods using two bits.

In accordance with an aspect of the present invention, a method ofadding Doppler enhancement to compression code typically formatted forgrayscale only, by using two bits of the data field to represent thescale of the remaining bits where said bits indicate one of the set ofscales comprising:

1. grayscale,

2. red scale, and

3. blue scale.

OBJECTS AND ADVANTAGES

Accordingly, beside the objects and advantages of the method describedabove, some additional objects and advantages of the present inventionare:

-   -   (a) to provide a method of compressing and decompressing video        signals so that the video information can be transported across        a digital communications channel in real time.    -   (b) to provide a method of compressing and decompressing video        signals such that compression can be accomplished with software        on commercially available computers without the need for        additional hardware for either compression or decompression.    -   (c) to provide a high quality video image without the blocking        and smearing defects associated with prior art lossy methods.    -   (d) to provide a high quality video image that suitable for use        in medical applications.    -   (e) to enhance images by filtering noise or recording artifacts.    -   (f) to provide a method of compression of video signals such        that the compressed representation of the video signals is        substantially reduced in size for storage on a storage medium.    -   (g) to provide a level of encryption so that images are not        directly viewable from the data as contained in the        transmission.    -   (h) to provide efficient encoding of Doppler enhanced images.    -   (i) to reduce the size of an encoded data buffer that contains        Doppler enhancement.    -   (j) to provide efficient encoding for video images that contain        distinguishable regions.    -   (k) to reduce the size of an encoded data representing a video        stream.    -   (l) to reduce the bandwidth required to transmit an encoded        video stream.    -   (m) to provide user control of compression methods.

DRAWING FIGURES

In the drawings, closely related figures have the same number butdifferent alphabetic suffixes.

FIG. 1 shows the high level steps of compression and decompression of animage.

FIG. 2A to 2H show alternatives for selecting a pixel value forencoding.

FIG. 2A shows the four channel format of a pixel.

FIG. 2B shows the three color components of a pixel.

FIG. 2G shows selection of a component of a grayscale pixel.

FIG. 2F shows a selection of the red component of a red scale pixel.

FIG. 3A shows the basic format of the ZLN variable encoding format

FIG. 3B shows an example of a code where N is 5 bits wide and U is 3bits wide.

FIG. 4A shows the flowchart for the compression method.

FIG. 4B shows an image and a corresponding stream of pixels.

FIG. 5A to 5C shows the formats for the run-length encoding of the RHNmethod.

FIG. 5D shows the ZLD format.

FIG. 5E shows the three formats of the three scales.

FIG. 5F shows an alternate embodiment of the grayscale format.

FIG. 5G shows the ZLD format embedded in the ZLN format.

FIG. 6 shows a series of codes and the resulting encoded stream.

FIG. 7 shows a series of codes and the resulting encoded stream of theRHN method.

FIG. 8A shows examples of variable formats.

FIG. 8B shows a format that preserves 9 bits of color.

FIG. 9 shows the flow chart for the decompression method.

FIG. 10 shows image stretching by interpolation.

FIG. 11A shows an example encode table.

FIG. 11B shows a corresponding grayscale decode table.

FIG. 11C shows a corresponding red scale decode table.

FIGS. 12A and 12B show machines for compressing and decompressing,respectively.

FIG. 12C shows a compressor and decompressor connected to a storagemedium.

FIG. 12D shows a compressor and decompressor connected to acommunications channel.

FIG. 13A shows elements of a compressor.

FIG. 13B shows an embodiment of an encoding circuit.

FIG. 13C shows a generic pixel sub-sampler.

FIGS. 13D through 13J show embodiments of pixel sub-samplers.

FIGS. 14A through 14C shows embodiments of a machine element forvariably altering the number of bits.

FIG. 15 shows elements of a decompressor.

FIG. 16A shows elements for setting width, height, frame rate,brightness, and contrast which are variably altered by a receiver.

FIG. 16B shows elements for setting the number of pixel bits that arevariably altered by a receiver.

FIG. 17 shows a lossless compression step for further compression of anencoded data buffer.

FIG. 18 shows images being enlarged by stretching.

Reference Numerals in Drawings  100 compression steps  110 sub-samplingstep  130 encoding step  140 encoded data  150 decompression steps  160decoding step  180 image reconstitution step  200 32 bit pixel value(four channel format)  202 blue channel  204 green channel  206 redchannel  208 alpha channel  210 24 bit pixel value  212 blue component 214 green component  216 red component  220 RGB averaging diagram  222blue value  224 green value  226 red value  228 averaged value  230 blueselection diagram  232 blue instance  234 green instance  236 redinstance  240 selected blue value  250 green selection diagram  260selected green value  270 red selection diagram  280 selected red value 290 grayscale pixel  292 grayscale blue  294 grayscale green  296grayscale red  298 selected grayscale value  299 filtered pixel value 300 N  301 U  302 W  310 pixel bit 7  312 pixel bit 6  314 pixel bit 5 316 pixel bit 4  318 pixel bit 3  320 pixel bit 2  322 pixel bit 1  324pixel bit 0  325 8 bit pixel  330 5 bit sample  332 sample bit 4  334sample bit 3  336 sample bit 2  338 sample bit 1  340 sample bit 0  3503 low order bits  360 formatted code  362 encoded bit 4  364 encoded bit3  366 encoded bit 2  368 encoded bit 1  370 encoded bit 0  380 3 bitcount value  400 encode flowchart  402 encode entry  403 encodeinitialization step  404 get pixel step  405 get value step  406 lookupencoded value step  408 compare previous  410 increment counter step 412 check count overflow  414 new code step  416 check end of data  418set done  420 counter overflow step  422 check done  428 encode exit 430 image  440 image width  450 image height  460 pixel stream  500code byte  501 S1  502 S0  503 S  505 E  510 flag bit  511Doppler/grayscale flag zero  512 don't care  514 grayscale value  515grayscale code  520 repeat code  521 Doppler/grayscale flag one  522blue/red flag zero  524 red scale value  525 red Doppler scale code  530count  531 second Doppler/grayscale flag one  532 blue/red flag one  534blue scale value  535 blue Doppler scale code  541 secondDoppler/grayscale flag zero  544 extended value  545 extended grayscalecode  550 data code  551 S1 in ZLN format  552 S0 in ZLN format  553 Sin ZLN format  554 E in ZLN format  555 C  557 X  560 wasted bits  565data bit 6  570 data bit 5  575 data bit 4  580 data bit 3  585 data bit2  590 data bit 1  595 data bit 0  610 decimal values  620 first value 622 second value  624 third value  626 fourth value  628 fifth value 630 sixth value  632 seventh value  640 binary code  650 first byte 651 first data  652 first count  653 second byte  654 second data  655second count  656 third byte  657 third data  658 third count  740 RHNbinary code  803 ZL3 format  804 ZL4 format  805 ZL5 format  808 ZL8format  809 ZL9 format  812 ZL12 format  820 ZL9C format  900 decodeentry  901 decode initialize step  902 get code step  908 decode lookupstep  909 check zero count  910 place pixel step  914 reset counter step 916 check length  918 decode exit  920 decode flowchart 1010 firstadjacent pixel 1012 second adjacent pixel 1014 first subsequent adjacentpixel 1016 second subsequent adjacent pixel 1052 interpolated pixel 1054interpolated pixel 1056 interpolated pixel 1058 interpolated pixel 1060interpolated pixel 1100 encryption table 1110 decryption table 1112grayscale red bits 1114 grayscale green bits 1116 grayscale blue bits1120 red scale decode table 1122 red scale red bits 1124 red scale greenbits 1126 red scale blue bits 1200 video frames 1205a first video frame1205b second video frame 1205n nth video frame 1210 compressor 1215video signal 1220 series of encoded data 1225a first encoded data 1225bsecond encoded data 1225n nth encoded data 1225 encoded data buffer1230a first received encoded data 1230b second received encoded data1230n nth received encoded data 1230 received encoded data 1235 encodeddata stream 1238 received encoded data (series) 1240 I/O device 1245input encoded data stream 1250 decompressor 1260a first decoded videoframe 1260b second decoded video frame 1260n nth decoded video frame1260 decoded video frame 1268 decoded video frames 1270 video sequence1280 storage medium 1290 communications channel 1310 video digitizer1320 path 1320 1330 video memory 1331 scan 1332 pixel index 1340 path1340 1350 encoding circuit 1360 path 1360 1370 encoded data 1380a 24 to5 bit sub-sampler 1380b 24-bit RGB to 5 bit sub-sampler 1380c 32-bit RGBto 5 bit sub-sampler 1380d color 9-bit sub-sampler 1380e YUV sub-sampler1380f 36-bit RGB to 24-bit sub-sampler 1380g 15-bit sub-sampler 1380pixel sub-sampler 1382 pixel extractor 1383 value path 1384 coder 1385path 1385 1390 data/count 1392 code index 1395 path 1395 1400 24-bit tovariable bit sub-sampler 1401 generic 3-bit sub-sampler 1402 generic4-bit sub-sampler 1403 generic 8-bit sub-sampler 1404 generic 10-bitsub-sampler 1410 number of bits selector 1420 number of bits indicator1430 36-bit to variable bit sub-sampler 1440 24/36 bit variable bitsub-sampler 1450 second selector 1460 selection logic 1470 selectionsignal 1510 decoding circuit 1520 decoded pixel values 1530 decoderpixel index 1540 image memory 1600 transmitter 1610 receiver 1615setting control path 1620 frame sub-sampler 1621 path 1621 1630 selectedframe 1632 pixel from frame 1640 transmitter pixel sub-sampler 1642 path1642 1650 run length encoder 1660 settings 1661 brightness 1662 contrast1663 height 1664 width 1665 frame rate 1670 frame selector 1675 frameselect indicator 1680 number of pixel bits setting 1690 alternatetransmitter 1700 run-length encoding step 1710 run-length encoded output1720 further lossless compression step 1730 further lossless compressionoutput 1800 unstretched frame 1810 enlarged image 1820 stretching step

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1—Compression and Decompression Steps

FIG. 1 illustrates a sequence of compression steps 100 and a sequence ofdecompression steps 150 of the present invention. The compression steps100 comprise a sub-sampling step 110 and an encoding step 130. Aftercompletion of the compression steps 100, a stream of encoded data 140 isoutput to either a storage medium or a transmission channel. Thedecompression steps 150 comprise a decoding step 160 wherein the streamof encoded data 140 is processed and an image reconstitution step 180.

FIGS. 2A to 2H—Selecting Pixel Values for Encoding

FIGS. 2A to 2G illustrate alternatives for selecting a pixel value forencoding. The sub-sampling step 110 (FIG. 1) includes sub-sampling of apixel value to obtain a variable selected number of bits.

Video digitizing hardware typical has the options of storing the pixelvalues as a 32 bit pixel value 200 or a 24 bit pixel value 210, shown inFIG. 2A and FIG. 2B, respectively. The 32 bit pixel value 200 iscomposed of a blue channel 202, a green channel 204, a red channel 206,and an alpha channel 208. Each channel contains 8 bits and can represent256 saturation levels for the particular color channel. For each channelthe saturation intensity value of zero represents the fully off state,and the saturation intensity value of “255” represents the fully onstate. A common alternative not shown is a sixteen-bit format where thethree color channels contain 5 bits each and the alpha channel is asingle bit. The present invention anticipates the use of the colorchannels of 16 bit pixel value is a manner substantially the same as the32-bit pixel value 200 except the number of bits per channel is 5instead of 8.

The 24-bit pixel value 210 is composed of a blue component 212, a greencomponent 214, and a red component 216. There is no component for thealpha channel in the 24 bit pixel value 210. Regardless of thestructure, the blue channel 202 is equivalent to the blue component 212,the green channel 204 is equivalent to the green component 214, and thered channel 206 is equivalent to the red component 216.

In the present invention, the 32 bit pixel value 200 alternative ispreferred due to the consistent alignment of 32 bit values in mostcomputer memories; however for simplicity of illustration the alphachannel 208 will be omitted in FIGS. 2C to 2G.

If the video signal is digitized in color, the three color componentsmay have different values. For example in FIG. 2C, a RGB averagingdiagram 220 illustrates a blue value 222 of 35 decimal, a green value224 of 15, and a red value 226 of 10. One alternative is to sub samplefrom 24 bits to 8 bits by averaging the three color values to obtain anaveraged value 228 that, in this example, has the value of 20:(10+15+35)/3=20. This will produce a grayscale image. Alternatively, acolor image can be preserved by sampling bits from each color component(see FIG. 8B).

FIG. 2D illustrates another alternative for selecting an 8 bit value ina blue selection diagram 230. In this example, a blue instance 232 hasthe value of 35, a green instance 234 has the value of 15, and a redinstance 236 has the value of 10. In this alternative the blue instance232 is always selected as a selected blue value 240.

FIG. 2E illustrates another alternative for selecting an 8 bit value ina green selection diagram 250. In this alternative the green instance234 is always selected as a selected green value 260.

FIG. 2F illustrates another alternative for selecting an 8 bit value ina red selection diagram 270. In this alternative the red instance 236 isalways selected as a selected red value 280.

If the video signal being digitized is grayscale, the three colorcomponents will have the same values. For example in FIG. 2G, agrayscale pixel 290 comprises a grayscale blue 292 with a value ofdecimal 40, a grayscale green 294 with a value of 40, and a grayscalered 296 with a value of 40. Because the values are all the same, itmakes no difference which grayscale color component is selected, aselected grayscale value 298 will have the value of 40 in this example.

The preferred embodiment of this invention uses the low order byte ofthe pixel value, which is typically the blue component as shown in FIG.2D.

FIG. 2H illustrates a filtered pixel value 299 of 8 bits that may beselected by one of the alternatives described above. In these examples,the filtered pixel value 299 is equivalent to items referenced bynumerals 228, 240, 260, 280, or 298. This reduction of the 32 bit pixelvalue 200 or the 24 bit pixel value 210 contributes a reduction in datasize of 4:1 or 3:1, respectively. This reduction recognizes that forsome images, such as medical images or grayscale images, no relevantinformation is lost.

For additional compression, the filtered pixel value 299 can variablyselect any number of bits. For example, selection of the mostsignificant four bits instead of all eight bits filters noise that mayshow up in the low order bits may be very suitable for an image such asone produced by an ultrasound medical device. An example of this isshown by ZL4 804 in FIG. 8A.

FIGS. 3A and 3B—Encoding Formats

Speed of compression and decompression may be enhanced if the algorithmsfit into computer memory native storage elements such as 8 bit bytes, 16bit words, or 32 bit double words, or some other size for which thecomputer architecture is optimized.

A grayscale image may be stored at a higher bit level than the actualvalues require. This may occur when an image is generated by an imagingtechnology such as radar, ultrasound, x-ray, magnetic resonance, orsimilar electronic technology. For example an ultrasound machine mayonly produce 16 levels of grayscale, requiring 4 bits of data per pixel,but the image digitizing may be performed at 8 to 12 bits per pixel. Inthis example, the low order bits (4 to 8) respectively provide nosignificant image data.

In the present invention, a fast and efficient compression and encodingmethod is implemented by using unused bits to store a repeat count forrepeated values.

The most significant N bits of the pixel value are selected where N 300is the number of significant bits (determined by data analysis or byuser selection). If N 300 is less than W 302, where W is a nativemachine data type such as 8 bit byte, 16 bit word, or 32 bit double wordor some other size for which the computer architecture is optimized,then W-N equals the number of unneeded bits, U 300. A repeat count, C,can contain a value from 1 to CMAX where CMAX is 2 to the power of U.For example, if U equals 4, C can be a number from 1 to 16. In practicethe maximum value will be encoded as a zero because the high order bitis truncated. In the example, decimal 16 has a binary value “10000” willbe stored as “0000”.

For example, when W is 8, value pairs for N and U could include withoutlimitation (2,6), (3,5), (4,4), (5,3), and (6,2). When W is 16, valuepairs for N and U could include without limitation (2,14), (3,13),(4,12), (5,11), (6,10), (7,9), (8,8), (9,7), (10,6), (11,5), (12,4),(13,3), and (14,2). When W is 32, value pairs for N and U could includewithout limitation all combinations of values pairs for N and U whereN+U equals 32 and N>1 and U>1. When W is not a multiple of 8, valuepairs for N and U could include without limitation all combinations ofvalues pairs for N and U where N+U equals W and N>1 and U>1.

FIG. 3A shows the encoded format where N 300 represent the N mostsignificant bits of the pixel value 299, U 301 represents the bits thatare not used for the data and are used for the repeat count, and W 302where W is the width of the encoded data and equal to sum of N and U. Asstated above W is preferably a native machine element.

FIG. 3B illustrates bit sub-sampling where N's 300 bit width is 5, U's301 bit width is 3, and W 302 is 8. The high order 5 bits 310-318 of an8 bit pixel 325 are extracted to form a five bit sample 330. The lower 3bits of 330 are ignored bits 350. In the formatted code 360, the ignoredbits 350 are replaced with the repeat count value 380.

Encoding

The most significant N bits of each pixel are selected from the image toobtain value V.

In the encryption embodiment of this invention V may be used to selectan encoded value, E, from the encoding table. E is also a N-bit value.The number of elements in the encode table 1100 (FIG. 11, shown as anencryption table), is 2 to the Nth power.

In the other embodiments of this invention V is used as E.

E is saved as the prior value, P. For each subsequent pixel, the encodedvalue, E, is obtained and compared to the prior value, P. If the priorvalue, P, is the same as E, then a repeat counter, C, is incremented;otherwise the accumulated repeat count, C, for the prior value, P, ismerged with P and placed in an array A that implements the encoded data140 (FIG. 1) buffer. For example, if W is 8 and N is 4 and C is 10, U is4, CMAX is 16, and ((P<<U)|C) is the merged value. If the repeat count,C, is greater CMAX, then CMAX is merged with P ((P<<U)|CMAX) and placedin the encoded data 140 (FIG. 1) buffer, A. CMAX is subtracted from Cand merged values are placed in A until C is less than CMAX. All pixelsare processed in this manner until the final value is compressed andencoded. The length, L, of the encoded data 140 (FIG. 1) is also placedin the encoded data 140 buffer.

FIG. 4A—Encode Flowchart

FIG. 4A illustrates the encode flowchart 400 which represents thedetails of the encryption embodiment of the encoding step 130 (FIG. 1)for the present invention.

The encoding begins at an encode entry 402. In an encode initializationstep 403, a prior value P is set to a known value, preferably decimal“255” or hexadecimal 0xFF, a repeat counter C is set to zero, an encodedlength L is set to 0, and a completion flag “Done” is set to a logicalvalue of false. Next, a get pixel step 404 obtains a pixel from theimage being encoded. At a get value step 405, a value V is set to the Nbit filtered pixel value 299 as derived from the pixel using one of themethods shown in FIG. 2C to 2G, preferably the fastest as explainedabove, and extracting the N most significant bits. At a lookup encodedvalue step 406, an encoded value E is set to the value of one of thecodes 1105 (FIG. 11A) of the encode table 1100 as indexed by V. (In thenon-encrypted embodiment of this invention, step 406 is bypassed becauseV is used as E) Next, a “compare previous” 408 decision is made bycomparing the values of E and P. If the values are the same, anincrement counter step 410 is executed and flow continues to the getpixel step 404 that obtains the next pixel from the image.

If the encode value E does not match the prior value P, then a checkcount overflow 412 decision is made. If the counter C is less than orequal to CMAX, then a new code step 414 is executed, otherwise a counteroverflow step 420 is executed.

At step 414, the counter C is masked and bit-wise OR-ed with P shiftedleft by U bit positions and is placed in the A at the next availablelocation as indexed by the encoded length L. Then, continuing insideflowchart step 414, L is incremented, the repeat count C is set to 1 andthe prior value P is set to E. After step 414, a “check end of data”decision is made by checking to see if there are any more pixels in theimage, and, if not, if the last value has been processed. Because thismethod utilizes a read ahead technique step 414 must be executed onemore time after the end of data is reached to process the lastrun-length. If there is more data in the image, flow continues to acheck of the completion flag “Done” at step 422. If the check indicatesthat the process is not completed, flow continues to step 404.

If the end of data is reached but the completion flag “Done” is stillfalse, flow continues to a set done step 418. At step 418, thecompletion flag “Done” is set to logical true, and flow continues todecision 412 where the last run-length will be output and flow willeventually exit through step 414, decision 416, decision 422, and thenterminate at encode exit 428.

It is possible for the repeat count C to become larger than CMAXrequiring more bits than allocated by this method. This situation ishandled by making the “check count overflow” 412 decision and executingthe “counter overflow” step 420. At step 420, the counter C is maskedand bit-wise OR-ed with P shifted left by U bit positions and is placedin the A at the next available location as indexed by the encoded lengthL. Then, continuing inside flowchart step 414, L is incremented, and therepeat count C is decrement by CMAX. After step 420, flow continues tothe “check count overflow” 412 decision. Thus when the encode value Erepeats more than CMAX times, multiple sets of repeat counts and encodedvalues are output to the encoded data 140 buffer.

This entire process is repeated for each image or video frame selectedduring optional image sub-sampling (see 110 in FIG. 1) and the encodedlength L is transmitted with the encoded data associated with eachframe. The encoded length varies from frame to frame depending on thecontent of the image being encoded.

FIG. 4B—Image and Pixel Stream

FIG. 4B illustrates an image and its corresponding stream of pixels. Arectangular image 430 is composed of rows and columns of pixels. Theimage 430 has a width 440 and a height 450, both measured in pixels. Inthis illustrative embodiment, pixels in a row are accessed from left toright. Rows are accessed from top to bottom. Some pixels in the imageare labeled from A to Z. Pixel A is the first pixel and pixel Z is thelast pixel. Scanning left to right and top to bottom will produce apixel stream 460. In the pixel stream 460, pixels A and B are adjacent.Also pixels N and O are adjacent even though they appear on differentrows in the image. If adjacent pixels have the same code the process inFIG. 4A will consider them in the same run.

Because the video signal being digitized is analog there will be someloss of information in the analog to digital conversion. The videodigitizing hardware can be configured to sample the analog data into theimage 430 with almost any width 440 and any height 450. The presentinvention achieves most of its effective compression by sub-sampling thedata image with the width 440 value less than the conventional 640 andthe height 450 value less than the convention 480. In a preferredembodiment of the invention, for use in a medical application with T1Internet transmission bandwidth, image dimensions are sub-sampled at 320by 240. However an image dimension sub-sampling resolution of 80 by 60may be suitable for some video application.

FIGS. 5A to 5C—Run-length Encoding Formats of the RHN Method

FIGS. 5A to 5C show use of a different structure than the presentinvention. FIGS. 5A to 5C show the formats for the run-length encodingof RHN. In FIG. 5A, a code byte 500, with its high order bit designatedas a flag bit 510.

FIG. 5B shows a repeat code 520 comprising a Boolean value one in itsflag bit 510 and a 7 bit count 530 in the remaining 7 low order bits.The seven bit count 530 can represent 128 values with a zerorepresenting “128” and 1 through 127 being their own value.

FIG. 5C shows a data code 550 comprising:

-   -   1. a Boolean value zero in its flag bit 510    -   2. two unused data bits: data bit 6 reference by 565 and data        bit 5 reference by 570, and    -   3. five bits, data bits 4 to 0, reference by 575, 580, 585, 590,        and 595, respectively.

FIG. 5C shows that in every byte of the RHN data code 550 two bits areunused and one bit is used for the flag bit, so that only five of theeight bits are used for data. The remaining three bits are wasted bits560. The present invention uses a different structure by placing therepeat count in bits that the RHN format would not have used for data(U). The corresponding ZLN format, ZL5 (where N is 5, U is 3, and W is8), always uses five bits for data and the remaining 3 bits for therepeat count. In practice, repeat counts are small and often can fit in3 bits, so this embodiment of the present invention will result insuperior compression performance over the RHN method.

In addition, the present invention provides for a larger count when thebit filtering is larger. For example, the alternate ZLN format whereeach byte contains 4 data bits, ZL4 (where N is 4 and U is 4), allowsfor a four bits of repeat count. For example, in practice, ZL4 issuperior to RHN on a typical ultrasound image containing 16 shades ofgray.

FIGS. 5D to 5G—Doppler Improvement of ZLN Format

The ZLN format for encoding video signals (see for example FIG. 3A) hasone disadvantage. When the video stream being compressed changes fromonly grayscale to grayscale overlaid with Doppler enhancement, thecolors of the Doppler red and blue scales are also converted tograyscale. A Doppler improvement aspect of the present inventionprovides a variable means of encoding the Doppler enhanced image with inthe data bits of a ZLN format.

FIG. 3A shows the ZLN format comprising N 300 and U 301 that make up adata element with a bit length of W 302.

The Doppler improvement aspect encodes the Doppler values in the N 300portion of the ZLN format. However the scope of this invention shouldnot be limited to using this technique with ZLN formats only as othercompression formats are anticipated by this invention.

Doppler Encoding Format

The Doppler enhanced grayscale image must be captured as color data (seeFIG. 2B). If the red, green, and blue values are the same, then thepixel is gray (e.g. FIG. 2G). If the red, green, and blue values are notequal, then the pixel is representing a red scale or blue scale value(e.g. FIG. 2F). By comparing the values of the red, green, and bluevalues, a red scale or blue scale value is determined.

In FIG. 5D, two bits, S 503, are used to indicate which scale the pixelis from. The high bit order bit, S1 501, is used to indicate that thevalue is a gray scale value: zero means grayscale (e.g. 515 in FIGS. 5Eand 541 in FIG. 5F), one means Doppler (e.g. 525 and 535 in FIG. 5E).The low order bit, S0 502, is used to indicate red scale or blue scale:zero means red scale (e.g. 525 in FIG. 5E), one means blue scale (e.g.535 in FIG. 5E). In the grayscale code 515, the value of the S0 bit is adon't care 512 and it can be coded as either a zero or a one. Incombination with the ZLN format, the remaining bits of W are used for arepeat count, C (FIG. 5G).

An alternate embodiment of this invention uses lookup tables ratherselecting the most significant bits. Instead of one encode (e.g. FIG.11A) and one decode table (e.g. FIG. 11B) as used in ZLN, a set oftables is used for each scale, gray, red, and blue, respectively. FIG.11C shows an example of a red scale decode table.

In an alternate embodiment, S0 is used as an additional bit of grayscaleresolution since S0 502 is not used in the grayscale case 545 (FIG. 5F).

In a method where W is the number of bits in a native machine data type,and N is the number of significant grayscale bits, two bits, S 503, areused to indicate which scale the pixel is from. The high bit order bitS1 501 is used to indicate that the value is a gray scale value: zeromeans grayscale 515, one means Doppler 525 and 535. The low order bit,S0 502, is used to indicate red scale or blue scale: zero means redscale 525, one means blue scale 535. In the ZLN combination, theremaining unused bits, U, are used for a repeat count, C, such that Wequals 2+N+U (FIG. 5G).

N bits of the blue component of the pixel value is used to index into ablue encode table to obtain the encoded value, E. In the ZLN method, ifE is repeated, a repeat count, C, is incremented.

X 557 is a concatenation of S1, S0, E, and C.

In this embodiment, like the ZLN method, the pixels of the frame areprocessed pixel by pixel as disclosed in reference to FIGS. 4A and 4B.When a value, E, is not repeated X is placed in the next location in thecompression array with a repeat count, C, equal to one.

Three decode tables that correspond to the grayscale, red scale, andblue scale encode tables contain the data necessary to reconstruct theoriginal value for the appropriate image. If the target color imageformat is W*4 bit color (FIG. 2A), then the decode table has W bits foralpha 208, red 206, green 204, and blue 202 each, respectively. If thetarget color image format is W*3 bit color, then the alpha value is notused. If the image is W bit grayscale than only the grayscale value isused to create the decompressed and decoded image.

To decode and decompress, the encoded data is processed W bits at a timeas X. S1, S0, E, and C are extracted from X with appropriate masks andshifts. If S1 is zero indicating grayscale, E is used as an index intothe gray scale decode table. If S1 is one indicating Doppler and S0 iszero indicating red scale Doppler, E is used as an index into the redscale decode table (FIG. 11C). If S1 is one indicating Doppler and S0 isone indicating blue scale Doppler, E is used as an index into the bluescale decode table (not shown, but with the proper values in the bluebit column 1126). The decoded value is placed into the decoded anddecompressed image. Each X is processed in order until the compressedarray length, L, has been processed.

FIG. 6—Encoded Data Stream

FIG. 6 shows a series of exemplary decimal values 610 comprising a firstvalue 620 equal to decimal 0, a second value 622 equal to 0, a thirdvalue 624 equal to 0, a fourth value 626 equal to 0, a fifth value 628equal to 0, a sixth value 630 equal to 2, and a seventh value 632 equalto 10. The value of zero is merely exemplary and could be any binaryvalue. After the encoding step 130 (FIG. 1), the corresponding encodeddata 140 (FIG. 1) would be compressed down to three bytes of binary code640 comprising a first byte 650, a second byte 653, and a third byte 656each containing a merged value and count, (651, 652), (654, 655), and(657, 658), respectively. The first data 651 has a binary value of“00000” which equals the exemplary repeated decimal value. The firstcount 652 has a binary value “101” which equals decimal fiverepresenting the run-length of the repeating value in the first five ofthe decimal values 610. The second data 654 has a binary value of“00010” which equals the non-repeated decimal value two. The secondcount 655 has a value of 1. The third data 657 has a binary value of“01010” which equals the non-repeated decimal value ten. The third count658 has a value of 1.

FIG. 7—RHN Codes and Encoded Stream

FIG. 7 shows the same series of decimal values 610 (FIG. 6) comprisingthe first value 620 equal to decimal 0, the second value 622 equal to 0,the third value 624 equal to 0, the fourth value 626 equal to 0, thefifth value 628 equal to 0, the sixth value 630 equal to 2, and theseventh value 632 equal to 10. After encoding by RHN, the correspondingencoded data 140 (FIG. 1) would be compressed down to four bytes of RHNbinary code 740.

The embodiment of the present invention shown in FIG. 6 only requiresthree bytes to encode the same data. In this example, the presentinvention is 25% better than the RHN format.

FIGS. 8A and 8B—ZLN Formats

The ZLN aspect of the present invention provides for variable formats.The values of N 300, U 301, and W 302 can be dynamically changed betweenframes. For ease of communication a format is named with the prefix “ZL”and a digit representing the value of N. For example, “ZL5” refers to aformat where bit width of N is equal to 5. There are multiple values ofU depending of the W. To also specify the bit width of U a hyphen and anumber can be appended. For example, “ZL5-13” represents a format whereN=5 and U=13. “ZL5-3” is a common format and may be imprecisely referredto as “ZL5.”

FIG. 8A shows a number of formats with adjacent labels: ZL3 803, ZL4804, ZL5 805, ZL8 808, ZL9 809, and ZL12 812. Data bits are representedby “D,” and count bits are represented by “C”.

FIG. 8B shows how the most significant 3 bits of each color component(216, 214, and 212 of FIG. 2B) are extracted and formatted in ZL9-7Cformat (the “C” append indicates that the color is preserved). Withthree red bits represented by “R”, three green bits represented “G” andthree blue bits represented by “B”.

Decoding

To decode the compressed array, the decoder has a decode table thatcorresponds with the encode table. For W*4 bit color pixels, the decodetable contains the appropriate alpha, red, green, and blue values. ForW*3 bit color pixels, the alpha value is not used. The compressed arrayis processed W bits at a time as X. The repeat count, C, is extractedfrom X by masking off the data value (C=X & (((2**N)−1)<<U)). Theencoded value, E, is extracted from X by masking off the count (E=X &((2**U)−1)). The encoded value, E may be used to index into thedecryption. The decoded pixels are placed in a reconstructed image andrepeated C times. Each element of the compressed array, A, is processeduntil its entire length, L, has been processed.

FIG. 9—Decode Flowchart

FIG. 9 illustrates the decode flowchart 920 which presents the detailsof the decryption embodiment of the decode step 160 (FIG. 1) and theimage reconstitution step 180 (FIG. 1).

The decoding begins at a decode entry 900. In a “decode initialization”step 901, a repeat counter C is set to one, an encoded length L is setto the value obtained with the encoded data 140 (FIG. 1), and an index Iis set to 0. Next, a “get code” step 902 obtains a signed byte X fromthe encoded data 140 (FIG. 1) array A. The index I is incremented. Thecount (for example the 3-bit count 380 as shown in FIG. 3B) is extractedfrom X by masking off the data bits and placed in the repeat counter C(C=X & ((2**N)−1<<U). The value of E is extracted from X by masking offthe count bits (E=X & (2**U)−1). In practice, the count mask and valuemask can be pre-computed with the following two lines of code in the Cprogramming language:

valueMask = −1 << U; countMask = ~valueMask;

In this illustrative decryption embodiment of the present invention,flow goes to a “decode lookup” step 908 where the value of E is used toindex into the decode table 1110 (FIG. 11, shown as decryption table) toobtain a pixel value V. In the other embodiments where E is notencrypted, E is used as V and step 908 is bypassed. Flow continues to a“check zero count” 909 decision.

The 909 decision always fails the first time ensuring that a place pixelstep 910 is executed. The place pixel step 910 places the pixel value Vin the next location of the decompressed image and decrements the repeatcounter C and returns to the 909 decision. The pixel value V is placedrepeatedly until C decrements to zero. Then the 909 decision branchesflow to a “reset counter” step 914. At step 914 the repeat counter isreset to 1.

Flow continues to the “check length” 916 decision where the index I iscompared to the encoded length L to determine if there are more codes tobe processed. If I is less than L flow returns to step 902, otherwisethe decode process terminates at a “decode exit” 918.

The entire decode process is repeated for each encoded frame image.

FIG. 10—Interpolation

FIG. 10 illustrates interpolation when two adjacent pixels 1010 and 1012and two subsequent row adjacent pixels 1014 and 1016 are stretched toinsert a new row and column of pixels.

Pixels 1052, 1054, 1056, 1058 and 1060 are inserted due to theenlargement of the image. Their values are calculated by averaging thevalues of the two pixels above and below or to the left or the right ofthe new pixel. A preferred sequence is calculation of:

-   1. 1052 between 1010 and 1012-   2. 1054 between 1010 and 1014-   3. 1058 between 1012 and 1016-   4. 1056 between 1054 and 1058    Pixel 1060 can be calculated on the interpolation for the subsequent    row.    FIG. 11—Encryption

By using corresponding encoding and decoding tables the data can beencrypted and decrypted without using actual values. Encryption providesa level of security for the encoded data 140 while in storage ortransit.

FIG. 11 shows an example of an encryption table 1100, where N is 3 and Wis 8, and a decryption table 1110, where N is 3 and U is 5.

The encode table 1100 is 2 to the power of N in length. If the targetcolor image format is W*4 bit color, then the decode table 1110 has Wbits for alpha, red, green, and blue each, respectively. If the targetcolor image format is W*3 bit color, then the alpha value is not used.If the image is W bit grayscale then only the grayscale value is used tocreate the decompressed and decoded image.

The corresponding table elements are mapped to each other. For example,0 could encode to 22 as long as the 22^(nd) element of the decode tablereturns (0xff<<24|0<<16|0<<8|0).

When these versions of the tables are used, the encode and decodeprocesses and their speed of execution are substantially the same butthe encoded data 140 (FIG. 1) becomes a cipher and has a higher level ofsecurity. It should be recognized by one with ordinarily skill in theart that there are other embodiments of the present invention withdifferent encryption/decryption table rearrangements.

FIGS. 12A through 12D—Compression and Decompression Devices

FIGS. 12A and 12B show devices for compressing and decompressing,respectively, a stream of video frames.

FIG. 12A shows a video signal 1215 being compressed and encoded by acompressor 1210 to form an encoded data stream 1235, which is sent to anI/O device 1240. The video signal 1215 comprises a series of videoframes 1200, shown as first video frame 1205 a, second video frame 1205b, . . . through nth video frame 1205 n. The encoded data stream 1235comprises a series of encoded data 1220, shown as first encoded data1225 a, second encoded data 1225 b, . . . , through nth encoded data1225 n.

FIG. 12B shows an input encoded data stream 1245 being received from anI/O device 1240, and then, decoded and decompressed by a decompressor1250 to form a video sequence 1270. The input encoded data stream 1245comprises received encoded data 1238, shown as first received encodeddata 1230 a, second received encoded data 1230 b, . . . , through nthreceived encoded data 1230 n. The video sequence 1270 comprises a seriesof decoded video frames 1268, shown as first decoded video frame 1260 a,second decoded video frame 1260 b, . . . , through nth decoded videoframe 1260 n.

FIG. 12C shows an embodiment where the I/O device 1240 of FIGS. 12A and12B is a storage medium 1280. The encoded data stream 1235 from thecompressor 1210 is stored in the storage medium 1280. The storage medium1280 provides the input encoded data stream 1245 as input to thedecompressor 1250.

FIG. 12D shows an embodiment where the I/O device 1240 of FIGS. 12A and12B is a communications channel 1290. The encoded data stream 1235 fromthe compressor 1210 is transmitted over the communications channel 1290.The communications channel 1290 provides the input encoded data stream1245 as input to the decompressor 1250.

FIGS. 13A through 13J—Compressor Details, Encoding Circuit, and BitwisePixel Sub-Samplers

FIG. 13A shows details of an embodiment of the compressor 1210, whichcomprises a video digitizer 1310, a video memory 1330, an encodingcircuit 1350, and encoded data 1370. Each video frame 1205 in the seriesof video frames 1200 is digitized by the video digitizer 1310 and storedalong path 1320 in the video memory 1330. The encoding circuit 1350access the digitized video frame via path 1340 and outputs the encodeddata 1370 along path 1360. The encoded data 1225 corresponding to eachvideo frame 1205 is then output from the compressor 1210.

FIG. 13B shows further details of an embodiment of the encoding circuit1350. A pixel sub-sampler 1380 scans each pixel from the digitized videoframe in the video memory 1330. A pixel index 1332 is used to drive ascan 1331 signal to select each pixel from the video memory, in apredetermined sequence. A novel aspect of the present invention is thatthe compression method can be accomplished with a single scan of thevideo memory for each frame. The pixel sub-sampler 1380 selects apredetermined number of bits from each pixel and outputs the data valuealong path 1385. Alternatively, the pixel sub-sampler 1380 encodes thesub-sampled data by using a lookup table similar to FIG. 11A. Differentpixel sub-samplers 1380 will be discussed in reference to FIGS. 13Cthrough 13J. The data/count 1390 unit increments the count each time theoutput of the pixel sub-sampler 1380 is the same; otherwise, when theoutput of the pixel sub-sampler 1380 is different (or when the counterreaches the maximum count value, the data and count are combined as acode and output along path 1395 to the encoded data 1225 for the framecurrently in the video memory 1330. The location of the code in theencoded data 1225 is selected by the code index 1392 signal.

FIG. 13C shows further details of a generic pixel sub-sampler 1380. Whena pixel is scanned from video memory along path 1340, it has an originalpixel bit width, P. A pixel extractor 1382 extracts a subset of bitsfrom each pixel with a value bit width, V, along value path 1383. Thevalue bit width V is less than the pixel bit width P. A coder 1384 takesthe V bits from the pixel path 1383 and outputs a code with an encodedbit width, E, as the data value along path 1385. One embodiment of thecoder is a null coder, or pass-through coder. Another embodiment of thecoder uses an encryption table to encrypt the data value as an encrypteddata value.

FIGS. 13D through 13J show embodiments of pixel sub-samplers.

FIG. 13D illustrates a 24 to 5 bit sub-sampler 1380 a, where the pixelbit width, P, is 24; the value bit width, V, output from the pixelextractor 1382 is 8 (see FIG. 2H); and the encoded bit width, E, outputfrom the coder 1384 is 5. In this embodiment, the extracted 8 bits couldbe any component of the grayscale (e.g. FIG. 2G) or the high order 8bits of the 24-bit value.

FIG. 13E illustrates a 24-bit RGB to 5 bit sub-sampler 1380 b, where thepixel bit width, P, is 24 divided into 8 bits of red, green, and blue(RGB, see FIG. 2B); the value bit width, V, output from the pixelextractor 1382 is 8; and the encoded bit width, E, output from the coder1384 is 5. In this embodiment, the extracted 8 bits could be an average(e.g. FIG. 2C) or one of the colors (e.g. FIG. 2D, 2E, or 2F).

FIG. 13F illustrates a 32-bit RGB to 5 bit sub-sampler 1380 c, where thepixel bit width, P, is 32 divided into 8 bits of red, green, blue, andalpha (see FIG. 2A); the value bit width, V, output from the pixelextractor 1382 is 8; and the encoded bit width, E, output from the coder1384 is 5. In this embodiment, the extracted 8 bits could be an average(e.g. FIG. 2C) or one of the colors (e.g. FIG. 2D, 2E, or 2F).

FIG. 13G illustrates a color 9-bit sub-sampler 1380 d, where the pixelbit width, P, is 24 divided into 8 bits each of red, green, and blue;the value bit width, V, output from the pixel extractors 1382 is 9; andthe encoded bit width, E, output from the coder 1384 is 9. In thisembodiment, the high order 3 bits of each color component are selected(e.g. ZL9C shown FIG. 8B).

FIG. 13H illustrates a YUV sub-sampler 1380 e, where the pixel bitwidth, P, is 24 divided into 8 bits for each of YUV; the value bitwidth, V, output from the pixel extractors 1382 is 8; and the encodedbit width, E, output from the coder 1384 is 5. In this embodiment, fourbits of the Y value is extracted and 2 bits of each of the U and Vvalues are extracted. This 8 bit value is further coded as a 5 bitvalue.

FIG. 13I illustrates a 36-bit RGB to 24-bit sub-sampler 1380 f, wherethe pixel bit width, P, is 36 divided into 12 bits each of red, green,and blue; the value bit width, V, output from the pixel extractors 1382is 24; and the encoded bit width, E, output from the coder 1384 is also24. In this embodiment, the high order 8 bits of each 12-bit colorcomponent are selected.

FIG. 13J illustrates a 15-bit sub-sampler 1380 g, where the pixel bitwidth, P, is 24 divided into 8 bits from each color component; the valuebit width, V, output from the pixel extractor 1382 is 15; and theencoded bit width, E, output from the coder 1384 is 15. In thisembodiment, the high order 5 bits of each 8-bit color component areselected.

FIGS. 14A through 14C—Variable Selection of Bit-wise Sub-sampling

FIGS. 14A through 14C show embodiments of a device for variably alteringthe number of bits.

FIG. 14A illustrates 24-bit to variable bit sub-sampler 1400. When apixel is scanned from video memory along path 1340, it has an originalpixel bit width, P, equal to 24 bits. These 24 bits are passed as inputto a number of sub-samplers. The variable number of bits is selected bya number of bits selector 1410 as indicated by a number of bitsindicator 1420 and outputs a code with an variable encoded bit width, E,as the data value along path 1385. A user at remote receiver 1610 setsthe number of bits indicator 1420 (see discussion regarding FIGS. 16Aand 16B). The variable bit sub-sampler comprises a generic 3-bitsub-sampler 1401, a generic 4-bit sub-sampler 1402, generic 8-bitsub-sampler 1403, and generic 10-bit sub-sampler 1404 which areembodiments of the generic sub-sampler shown in FIG. 13C with specificvalues for E. The variable bit sub-sampler further comprises nestedsub-samplers: the 24 to 5 bit sub-sampler 1380 a of FIG. 13D, the 1380 dof FIG. 13G, and the 15-bit sub-sampler 1380 g of FIG. 13J. This isillustrative of the types of bit sub-samplers that can be variablyselected.

Likewise, FIG. 14B illustrates a 36-bit to variable bit sub-sampler1430, where P is 36 and the number of bit that can be selected are 12,15, or 24, respectively.

FIG. 14C shows that the 24-bit to variable bit sub-sampler 1400 of FIG.14A and the 36-bit to variable bit sub-sampler 1430 of FIG. 14B can befurther combined to form at 24/36 bit variable bit sub-sampler 1440where a second selector 1450 is used to selected either the 24 bitinputs or the 36 bit inputs using selection logic 1460 that alsoreceives the number of bits indicator 1420. A selection signal 1470enables either the output of 24-bit to variable bit sub-sampler 1400 orthe output of 36-bit to variable bit sub-sampler 1430. Sub-samplers 1400and 1430 both receive the number of bits indicator 1420 as shown in FIG.14A and FIG. 14B. In this way any number of bits may reasonably beselected from either a 36 or 24-bit pixel bit width.

FIG. 15—Decompressor Elements

FIG. 15 shows details of an embodiment of the decompressor 1250, whichcomprises a decoding circuit 1510 which inputs received encoded data1230 and outputs decoded pixel values 1520 to an image memory 1540. Adecoder pixel index 1530 selects the location in the image memory 1540to store the decoded pixels values 1520. The image memory 1540 deliverseach decoded video frame 1260 to the video display.

FIGS. 16A and 16B—Parameters Altered by a Remote Receiver

FIG. 16A shows a system for setting width, height, frame rate,brightness, and contrast in a transmitter 1600 which are variablyaltered by a receiver 1610. The receiver sends commands to thetransmitter 1600 via setting control path 1615. The commands alter thetransmitter settings 1660.

The settings 1660 include brightness 1661, contrast 1662, height 1663,width 1664, and frame rate 1665. The brightness 1661, contrast 1662,height 1663, and width 1664 setting alter the attributes of each frameas it is digitized in a frame sub-sampler 1620. The brightness 1661 andcontrast 1662 settings alter the video digitizer 1310 (FIG. 13A) as itsenses the video frame. The height 1663 and 1664 allow for optionallyselecting a subset area of each frame; this is area sub-sampling.Alternatively, height 1663 and 1664 allow for optionally selecting asubset of pixels from an array of pixels that make up a single frame, byskipping pixels in a row or by skipping rows; this is imagesub-sampling. The frame rate 1665 setting alters the frame selector 1670which drives the frame select indicator 1675 to optionally sub-sampleframes from a sequence of video frames; this is frame sub-sampling.

The frame sub-sampler 1620 outputs a selected frame 1630 along path1621. The transmitter pixel sub-sampler 1640 scans the selected frame1630 getting each pixel from frame 1632 and outputs data values alongpath 1642 to a run length encoder 1650. The encoded data stream 1235 isthen transmitted to the remote receiver 1610.

FIG. 16B shows additional elements of a system for setting the number ofpixel bits in an alternate transmitter 1690 which is variably altered bya receiver 1610. The receiver sends commands to the transmitter 1600 viasetting control path 1615. The commands alter the transmitter settings1660. The settings include a number of pixel bits setting 1680 whichaffect the number of bits selected by the transmitter pixel sub-sampler1640. The pixel sub-sampler 1640 could be any pixel sub-sampler, forexample, see FIG. 13C through 13J and 14A through 14C. The transmitterpixel sub-sampler 1640 scans the selected frame 1630 (as in FIG. 16A)getting each pixel from frame 1632 and outputs data values along path1642 to a run length encoder 1650. The encoded data stream 1235 is thentransmitted to the remote receiver 1610.

These embodiments illustrate the novel feature of the present inventionof allowing a user at a remote receiver 1610 to control aspects of thetransmitter 1600 or 1690 from a remote location, including brightness,contrast, frame dimensions, frame rate, image area, and the type ofcompression used.

FIG. 17—Further Lossless Compression Step

FIG. 17 shows a lossless compression step for further compressing anencoded data buffer. After a run-length encoding step 1700 in thetransmitter, a run-length encoded output 1710 can be further processedwith a further lossless compression step 1720 resulting in furtherlossless compression output 1730. The further lossless compression step1720 could be implemented as a variable length coding, arithmeticcoding, or other compression step known in the art.

FIG. 18—Image Stretching

FIG. 18 shows images being enlarged by stretching. An unstretched frame1800 is stretched during stretching step 1820 resulting in an enlargedimage 1810. When a frame is image sub-sampled or area sub-sampled, theremaining data can be stretched to fill the full display area on thereceiver 1610. This results in an interpolated image or magnified image,respectively.

Distinguishable Characteristics

Most video images contain regions that are distinguishable from theother pixels that make up an image. Sometimes the distinguishingcharacteristic is the importance of the region to the viewer. In medicalimaging such as ultrasound, the generated image in the center of thedisplay may be of most importance to the viewer. Sometimes thedistinguishing characteristic is the compressibility of the regions.Sometimes the distinguishing characteristic is the color depth of theregions. Sometimes the distinguishing characteristic is the rate ofchange of the regions.

A region of solid color or grayscale value compresses more efficientlythan a series of varying values. This is true of the ZLN compressionmethod. If the regions are distinguished based on their compressibility,different compression methods can be applied to each region.

Grayscale pixel values can be stored in 8 bits while the correspondingquality of color pixel is often stored in 24 or 32 bits. If the regionsare distinguished based on their storage requirements (also known ascolor depth, or bit depth), a significant space or bandwidth saving canbe made.

A Doppler enhanced image such as a weather map or an ultrasound medicalimage is synthesized by the Doppler circuitry. In the case of a weathermap, the underlying image does not change but the Doppler enhancedvelocity scales do change from frame to frame. In the case of Dopplerenhanced ultrasound image, the underlying grayscale ultrasound imagechanges more frequently than the circuitry can calculate and display theDoppler information. If the Doppler and non-Doppler regions areprocessed separately the overall effective compression sizes andtransmission times can be reduced.

Automatic Switching between Grayscale Only and Doppler Enhanced Formats

As disclosed, for example in U.S. application Ser. No. 09/321,922regarding its FIG. 2, the video image capture device receives a streamof video images (1200) from a video source. The compressor 1210 isconfigured to compress the stream of video images 1200 thereby creatinga compressed stream of video images (e.g. 1235). This is also shown inFIG. 12C. Video parameters such as the compression algorithm areincluded within the video settings. In one embodiment of this invention,the compressor, which is determining the scale of each pixel, can countthe number of Doppler enhanced pixels in each frame, or image, of thevideo stream. As discussed above, whether a pixel is grayscale orDoppler enhanced is determined by comparing the red, green, and bluecomponent values. If no Doppler pixel is found in an image, a standardgrayscale format, such as ZLN format, can be used as the compressionmethod of the compressor (i.e. Doppler enhanced encoding can beautomatically switched off). When a Doppler enhanced pixel is found in asubsequent frame of the video stream by the same counting mechanism, thecompressor can automatically be switched to use the Doppler enhancedformat described above. The compressor will continue to use thiscompression method until the counting mechanism fails to detect aDoppler enhanced pixel, then the grayscale only compression method canbe switched on again.

ADVANTAGES

Noise Filtering and Image Enhancement

The removal of the least significant bits of pixel values results inhigh quality decompressed images when the original image is generated byan electronic sensing device, such as an ultrasound machine, which isgenerating only a certain number of bits of grayscale resolution. Byvariably altering the number of most significant bits, various filterscan be implemented to enhance the image quality. Such a noise filter canbe beneficial when the image is generated by an imaging technology suchas radar, ultrasound, x-ray, magnetic resonance, or similar technology.Variations can be made to enhance the perceived quality of thedecompressed image. Therefore, altering the number of data bits selectedand altering the width of the repeat count is anticipated by thisinvention and specific values in the examples should not be construed aslimiting the scope of this invention.

Dynamic Variable Formats

While a video stream is being viewed, a viewer on the decoding end ofthe transmission can vary the settings for the compressor. Differenttradeoffs between image spatial and temporal quality can be made. As thecontents of the video signal change an appropriate format can beselected. Control signals can be sent back to the compressor via acommunications link.

While a video stream containing Doppler enhancement is being viewed, aviewer on the decoding end of the transmission can vary the settings forthe compressor. Different tradeoffs can be made. For example, moreDoppler detail can be chosen with slower frame rate.

Automatic Switching

If no Doppler pixel is found in an image, a standard ZLN format can beused (i.e. Doppler enhanced encoding can be automatically switched off).When Doppler enhancement again appears in the video stream (asrecognized by the detection of a Doppler pixel in a frame), the Dopplerenhanced encoding can automatically be switched on again.

Execution Speed

The preferred embodiment of this invention uses a number of techniquesto reduce the time required to compress and decompress the data.

The methods require only a single sequential pass through the data. Boththe compression steps 100 and the decompression steps 150 access a pixelonce and perform all calculations.

When selecting the filtered pixel value 299, the preferred embodimentselects the low order byte from the 32 bit pixel value 200 or the 24 bitpixel value 210 so that an additional shift operation or addressingoperation is avoided.

The shift operation is a fast and efficient way to convert a byte orword to the filtered pixel value 299.

General Purpose

The lossless compression of the sampled data achieved by a preferredembodiment of the present invention results in high quality videostreams that have general purpose application in a number of areasincluding, without limitation, medical, aviation, weather traffic, videoconferencing, surveillance, manufacturing, rich media advertising, andother forms of video transmission, storage, and processing.

Lossless Nature/No Artifacts

Once the analog signal is sub-sampled and filtered to select a filteredpixel value that eliminates some of the real world defects, the methodsof the present invention compress and decompress the data with noirreversible data loss. Unlike JPEG and MPEG, the decompressed imagenever suffers from artificially induced blocking or smearing or otherartifacts that are result of the lossy compression algorithm itself. Asa result even a small sub-sample of the image remains clear and true tothe perceived quality of the original image.

Superior Features over RHN Format

When compared against the RHN format, the format and methods of thepresent invention provide a number of advantages, including, but notlimited to, faster speed and smaller size of encoded data, betterperformance for both medical and typical video images, and a typicallycloser representation of the original video signal.

Superior Features over ZLN Format

When compared against the ZLN format, the format and methods of theDoppler improvement aspect of the present invention provide a number ofadvantages, including, but not limited to, a typically closerrepresentation of the original video signal. As stated above, whencompared to a method using all three or four color components, theDoppler improvement aspect of the present invention provides theadvantages of efficient encoding of Doppler enhanced images and reducedsize of an encoded data buffer that contains Doppler enhancement.

Optimal Encoding

The present invention also provides a method for separating a videoimage into distinguishable regions. Each region can be encoded,compressed, and transferred in a manner that is optimal for itsdistinguishing characteristics.

Reduced Size

The present invention may also reduce the size of an encoded videostream. The reduced size saves in the usage and cost of storage devicesand computing and networking resources.

Reduced Bandwidth

The present invention may also reduce the bandwidth required to transfera compressed video stream. Both transfers within a computer system to astorage device, such as a hard disk, tape drive, and the like, andtransfers between a transmitter and a receiver over a network, such as aLAN, the Internet, a television network, and the like, are improved.

This improved bandwidth allows for the regions of interest to bedisplayed at a higher quality of resolution and motion while reducingthe requirements and cost of a high bandwidth connection or a connectionwith reduced traffic. For example, the present invention allows a videosteam that previously had to be sent over a 1.54 Mb T1 line to be sentover a much less costly and much more prevalent DSL, cable modem, or 56Kb modem connection.

Efficient Doppler Handling

The present invention also provides efficient methods for handlingDoppler enhanced images. This allows for lower cost storage of weather,air traffic, and medical images. It also allows for enhanced quality ofimages.

CONCLUSION, RAMIFICATION, AND SCOPE

Accordingly, the reader will see that the compression and decompressionsteps of the present invention provide a means of digitally compressinga video signal in real time, a means of digitally compressing Dopplerenhanced video signal in real time, communicating the encoded datastream over a transmission channel, and decoding each frame anddisplaying the decompressed video frames in real time.

Furthermore, the present invention has additional advantages in that:

-   1. it provides a means of filtering real world defects from the    video image and enhancing the image quality;-   2. it allows for execution of both the compression and decompression    steps using software running on commonly available computers without    special compression or decompression hardware;-   3. it provides decompressed images that have high spatial quality    that are not distorted by artifacts of the compression algorithms    being used;-   4. it provides a variably scalable means of video compression and of    adding Doppler enhancement; and-   5. it provides a means for reducing the space required in a storage    medium.

While my above descriptions contain several specifics these should notbe construed as limitations on the scope of the invention, but rather asexamples of some of the preferred embodiments thereof. Many othervariations are possible. For example, bit ordering can be altered andthe same relative operation, relative performance, and relativeperceived image quality will result. Also, these processes can each beimplemented as a hardware apparatus that will improve the performancesignificantly. In another example, frame differencing may be applied tothe input stream to select a subset of a frame to be the original image,or a post processing step could be added to remove artifacts introducedby a particular decompression method.

Accordingly, the scope of the invention should be determined not by theembodiments illustrated, but by the appended claims and their legalequivalents.

1. A method comprising: determining, by an encoder, whether a pixel of aDoppler enhanced grayscale image is a grayscale pixel or a Dopplerenhancement pixel, by determining a color scale of the pixel, wherein aDoppler enhanced grayscale image comprises grayscale pixels and Dopplerenhancement pixels, and wherein a Doppler enhanced grayscale image iscaptured as a color image; setting, by the encoder, a flag to indicatewhether the pixel has a grayscale value or is a Doppler enhancementpixel, based on a result of said determining; and generating andoutputting, by the encoder, a codeword that encodes the pixel value andthe flag.
 2. The method of claim 1, further comprising determining, bythe encoder, a Doppler scale of the pixel, on determining that the pixelis a Doppler enhancement pixel.
 3. The method of claim 2, wherein theflag is a first flag, the method further comprises setting, by theencoder, a second flag to indicate the determined Doppler scale, andgenerating and outputting comprises generating and outputting a codewordthat encodes the pixel value, the first flag and the second flag.
 4. Themethod of claim 3, wherein setting a first flag comprises setting afirst bit of a data word and setting a second flag comprises setting asecond bit of the data word.
 5. The method of claim 3, whereingenerating comprises retrieving the codeword from a table.
 6. The methodof claim 2, wherein determining a Doppler scale of the pixel comprisesdetermining a selected one of a red scale or a blue scale.
 7. The methodof claim 1, wherein the image is a selected one of a medical image or aweather image.
 8. The method of claim 1, wherein the pixel comprises aplurality of color components, and determining comprises comparingvalues of the color components.
 9. The method of 8, wherein determiningcomprises determining the pixel as a grayscale pixel if the colorcomponent values are equal, and determining the pixel as a Dopplerenhancement pixel if the color component values are not equal.
 10. Themethod of claim 1 further comprising: counting, by the encoder, a numberof Doppler enhanced pixels in the image; and turning on, by the encoder,Doppler enhanced encoding when a result of the counting is greater thanzero.
 11. The method of claim 10, further comprising turning on, by theencoder, grayscale encoding when the result of the counting is zero. 12.The method of claim 1, wherein generating comprises retrieving thecodeword from a table.
 13. The method of claim 1, wherein the image is avideo frame.
 14. An apparatus comprising: an encoder configured todetermine a color scale of a pixel of a Doppler enhanced grayscaleimage, to determine whether the pixel is a grayscale pixel or a Dopplerenhancement pixel, set a flag to indicate whether the pixel has agrayscale value or is a Doppler enhancement pixel, based on a result ofthe determination, generate and output a codeword that encodes the pixelvalue and the flag; and a transmitter coupled with the encoder andconfigured to transmit the codeword; wherein a Doppler enhancedgrayscale image comprises grayscale pixels and Doppler enhancementpixels; and wherein a Doppler enhanced grayscale image is captured as acolor image.
 15. The apparatus of claim 14, wherein the encoder isfurther configured to determine a Doppler scale of the pixel, ondetermination that the pixel is a Doppler enhancement pixel.
 16. Theapparatus of claim 15, wherein the flag is a first flag, and the encoderis further configured to set a second flag to indicate the determinedDoppler scale, generate and output a codeword that encodes the pixelvalue, the first flag and the second flag.
 17. The apparatus of claim16, wherein the encoder is configured to set a first bit of a data wordto indicate whether the pixel has a grayscale value or is a Dopplerenhancement pixel and set a second bit of the data word to indicate aDoppler scale of the pixel.
 18. The apparatus of claim 16, furthercomprising a storage device configured to store a table that includesthe codeword.
 19. The apparatus of claim 14, wherein the pixel comprisesa plurality of color components, and the encoder is configured tocompare values of the color components to determine whether the pixelhas a grayscale pixel value or a Doppler enhancement pixel.
 20. Theapparatus of 19, wherein the encoder is configured to determine thepixel as a grayscale pixel if the color component values are equal, anddetermine the pixel as a Doppler enhancement pixel if the colorcomponent values are not equal.
 21. The apparatus of claim 14 furthercomprising a counter coupled with the encoder, and configured to count anumber of Doppler enhanced pixels in the image.
 22. The apparatus ofclaim 21 wherein the encoder is further configured to turn on Dopplerenhanced encoding when a result of the count is greater than zero, andturn on grayscale encoding when the result of the count is zero.
 23. Anarticle of manufacture comprising: a non-transitory computer-readablestorage device; and a plurality of programming instructions stored inthe storage device, and configured to enable an apparatus to perform anumber of operations, in response to execution of the programminginstructions by the apparatus, wherein the operations include:determining whether a pixel of a Doppler enhanced grayscale image is agrayscale pixel or a Doppler enhancement pixel, by determining a colorscale of the pixel, wherein a Doppler enhanced grayscale image comprisesgrayscale pixels and Doppler enhancement pixels, and wherein a Dopplerenhanced grayscale image is captured as a color image; setting a flag toindicate whether the pixel has a grayscale value or is a Dopplerenhancement pixel, based on a result of said determining; and generatingand outputting a codeword that encodes the pixel value and the flag. 24.The article of claim 23, wherein the operations further comprisedetermining a Doppler scale of the pixel, on determining that the pixelis a Doppler enhancement pixel.
 25. The article of claim 24, wherein theflag is a first flag, the operations further comprise setting a secondflag to indicate the determined Doppler scale, and generating andoutputting comprises generating and outputting a codeword that encodesthe pixel value, the first flag and the second flag.